some OS's have portable tools that allow:
o building of populated file systems
(given a template construct a non empty filesystem
possibly as a simple file)
o manipulate an unmounted file system
(given a a raw device (or just a file),
add/move/remove files)
Does NetBSD have similar tools (for manipulating a raw ufs)?
Currrently, no, and it's not clear to me that it's worthwhile.
If you're thinking of what I expect you are, you could network boot
and build a file system using native tools.